In order to electrically connect a wind turbine generator to a power grid, several power connection arrangements may be used. A typical power connection arrangement (e.g. for a full scale converter based turbine) comprises a generator side converter, a DC (direct current) link, a grid side converter and a grid transformer which are placed between the wind turbine generator and the power grid in this order. The generator side converter controls the generator power and transfers it to the grid through the DC-link and the grid side converter. The control of the grid side converter should be carried out such that the quality of the electrical power supplied to the grid is kept within predetermined tolerance ranges even during abnormal grid voltage conditions like symmetric/asymmetric voltage dip and swell conditions. In case of abnormal grid voltage conditions, support of reactive power may be needed to fulfil the grid requirements. That is, the power which is supplied to the grid needs to have, besides an active power component, a reactive power component. During normal working conditions, the reactive power component might be required depending on the grid support requirement. The reactive power support is getting increasingly important due to the grid code requirements that are getting stricter along the increase of wind power penetration.
It is therefore an object to provide a method of controlling a wind turbine which is capable of supporting the demanded power quality even during abnormal voltage conditions. Further, this method should be easy to realize.